1. Field of the Invention
The present invention relates to a display device comprising a display panel, a video driver and a timing generator. And, more particularly, the invention relates to a driving control technique for a display device adopting a simultaneous multiple-pixel sampling method.
2. Description of Related Art
The simultaneous multiple-pixel sampling method is dominant as a system for driving a display panel which is represented by an active-matrix liquid crystal display panel or the like, and its one example is disclosed in Japanese Patent Laid-open No. Hei 4 (1992)-116687. According to this method, a color display panel has a plurality of data lines which are disposed in parallel with one another vertically and are so arranged that successive three lines thereof form a set of red (R), green (G) and blue (B). The display panel also has a plurality of gate lines disposed in parallel with one another horizontally, and pixel electrodes connected via switching elements respectively to the intersections of the data lines and the gate lines. The pixel electrodes are so disposed that alternate ones in the vertical (column) direction have a positional deviation corresponding to a half of the pixel array pitch in the horizontal (row) direction, and vertically alternate ones are connected to the left and right data lines alternately. In addition, the color display panel also has a plurality of horizontal switches provided correspondingly to the data lines, and further three video lines connected via the horizontal switches to the data lines of the individual colors so as to receive R, G, B video signals supplied from the video driver. In this configuration, a horizontal driving circuit is provided for simultaneously controlling the horizontal switches per set of R, G, B, so that three R, G, B pixels are simultaneously driven for sampling. And a delay means is provided in the video driver for relatively giving a predetermined delay, which corresponding to the pixel pitch, to each of the R, G, B video signals supplied to the three video lines. Thus, the delay corresponding to the pixel pitch is relatively given to the R, G, B video signals, and the on/off actions of the horizontal switches per set of R, G, B are controlled simultaneously, so that it becomes possible to curtail the number of required stages of the horizontal driving circuit (e.g., shift registers) for driving the horizontal switches, hence simplifying the configuration with a reduction of the power consumption to thereby display a satisfactory color picture. Since the on/off actions of the R, G, B horizontal switches are controlled simultaneously by sampling pulses outputted from the shift registers, the number of the required shift registers can be reduced to 1/3, and the frequency of a horizontal transfer clock signal Supplied from the timing generator is lowered also to 1/3.
In any display device adopting the simultaneous multiple-pixel sampling method, there exists a problem in principle that a phenomenon of vertical streak ghost is caused under specific conditions. For example, such a ghost occurs when changes of video signals supplied to its display panel are slow and the change time is longer than the sampling time allocated to the multiple pixels. Even when the change time of video signals supplied to the display panel is sufficiently fast, there still occurs a ghost if the closing of any horizontal switch incorporated in the display panel is coincident in timing with the change region. The first condition is prone to be induced readily if the number of horizontal pixels is increased in the display panel and the frequency .sup.f HCK of a horizontal transfer clock signal is higher. And the second condition, which is induced or not in dependence on the frequency .sup.f HCK, is rendered more prone to occur with a rise of the frequency .sup.f HCK. In any of the conventional display panels known heretofore, the number of pixels is not so many that the above conditions are satisfied. Namely, the frequency .sup.f HCK is not so high. And the horizontal driving circuit incorporated in the display panel operates substantially at a fixed frequency .sup.f HCK in most cases, so that there never occurs a state where the horizontal driving circuit is placed in the above-described specific conditions while being dislodged from the optimal condition once set. However, in any of the superhigh-precision display panels developed of late extensively, it is extremely difficult to find the optimal condition while excluding the aforementioned specific conditions and still ensuring a certain margin. In other words, extraordinarily strict specifications are required in design. And in displaying pictures of various signal standards including a 16:9 aspect ratio and so forth correspondingly to multimedia, the frequency of the horizontal transfer clock signal in the display panel is changed in diversified ways to consequently bring about further difficulties in finding the optimal condition.